1. Field of the Invention
The present invention relates to a semiconductor package such as a ball grid array (BGA) package.
2. Description of the Related Art
Recently, electronic products, such as personal computers (PC), cellular phones, and camcorders, become smaller and require higher performance. As a result, a semiconductor package having small size, large capacity, and fast processing speed is also required. To meet this requirement, a semiconductor package has evolved from a conventional through-hole type package, such as a dual in-line package (DIP), into surface mounting type packages, such as a thin small out-line package (TSOP), a thin quad flat package (TQFP), and a ball grid array (BGA) package.
In the BGA package, an insulating substrate, which includes copper printed circuit patterns formed on an upper region or on upper and lower regions, is used for the semiconductor package instead of a conventional lead frame.
FIGS. 1 and 2 are sectional views of a conventional ball grid array (BGA) package. FIG. 1 is a sectional view of a conventional BGA package having a double layer substrate. Hereinafter, the structure of the BGA package according to its manufacturing process will be described. Referring to FIG. 1, a semiconductor chip 6 singularized from wafers is prepared by a wafer sawing process. Subsequently, a die attach process, that is, a step of attaching the semiconductor chip 6 to a substrate 10 using an adhesive 5, is performed.
Printed circuit patterns 14 formed of copper are disposed on upper and lower regions of the substrate 10 and are connected to each other through a micro-via hole 9 and are in turn connected to a solder ball 13 on a lower region of the substrate 10. Also, solder masks 1 and 11 are formed on the upper and lower regions of the substrate 10, respectively, for preventing a short circuit between the printed circuit patterns 14 and for easily bonding the solder ball 13. The inside of the substrate 10 is formed of plastic resin such as polyimide. A wire bonding process is performed on the substrate 10 to connect a bond pad (not shown) of the semiconductor chip 6 to each of bond fingers 2 and 3 of the substrate 10. Reference numerals 2 and 3 denote a bond finger connected to the solder ball and a bond finger connected to ground, respectively.
Subsequently, an encapsulation process for protecting the semiconductor chip 6 and a gold wire 4 from the external environment and shock is performed using an epoxy mold compound (EMC) as an encapsulant 7. Next, the solder ball 13 is attached to a solder ball pad 8 disposed under the substrate 10. Lastly, a strip-shaped unit BGA package is separated as an individual BGA package by a cutting process.
FIG. 2 is a sectional view of a conventional BGA package having a single layer substrate. Referring to FIG. 2, a printed circuit pattern 14 including a bond finger 2 on an insulating layer 12, such as polyimide, is formed only on a single surface of the substrate 10′. Thus, a solder ball pad 8 under the substrate 10′ is formed by punching the insulating layer 12 of the substrate 10′. The other elements have the same structure as those of the BGA package using the double layer of FIG. 1. Reference numerals 4, 5, 6, 7, and 13 denote a gold wire formed by wire bonding, an adhesive, a semiconductor chip, an encapsulant, and a solder ball, respectively.
FIG. 3 is a plan view illustrating the problems of the BGA manufacturing process in accordance with the prior art. First, referring to FIG. 3, terms used in the description of the present invention will be defined as follows.
A bond pad 15 is formed on a semiconductor chip 6 to connect integrated internal circuits to an external area of the semiconductor chip 6 by wire bonding. A bond finger 2 is formed on a package substrate 10. The bond finger 2 is electrically connected to the bond pad 15 by a gold wire 4. A solder ball pad 8 is formed on the substrate 10 to attach solder balls, i.e., external connecting terminals, in a semiconductor package, such as a BGA package. Also, a copper printed circuit pattern 14 is disposed on upper and/or lower regions of the substrate 10. In the case of a BGA package having the single layer substrate, the printed circuit pattern 14 connects the solder ball pad 8 to the bond finger 2.
In general, if the design of the semiconductor chip 6 is changed slightly, the number of added bond pads 20 for performing a new function in the semiconductor chip 6 increases from one to three or four. Thus, in order to package the semiconductor chip 6, the design of the substrate 10, which is used as a frame material, must be changed as well. However, if the existing substrate can be used by utilizing a redundant bond finger 21 and a redundant solder ball pad 22 formed on the substrate 10 without changing the design of the substrate 10, manufacturing cost can be reduced and a conventional process parameter can be used.
FIG. 3 illustrates that, unlike wire-bonding the added bond pad 20 to the redundant bond finer 21, it is difficult to connect the redundant bond finger 21 to the redundant solder ball pad 22. More particularly, in case of the BGA package having the single layer substrate, because the redundant solder ball pad 22 is surrounded by another printed circuit pattern 14′, it is nearly impossible for the redundant solder ball pad 22 to be connected to the redundant bond finger 21.
For these reasons, if the design of the semiconductor chip 6 is changed slightly, it is difficult to make connections between the added bond pad 20 and the redundant solder ball pad 22 using the existing substrate 10. Thus, in case of the single-layer substrate, the substrate design must be changed to a double-layer substrate with an additional micro-via hole formed therethrough. Also, in case of the multi-layer substrate, such as the double-layer substrate, the number of layers of the substrate must be increased with additional micro-via holes formed therethrough.
In this case, because there are the added costs of changing the design of the substrate and manufacturing of the semiconductor package, and because the substrate manufacturing process becomes more complicated, the overall BGA package manufacturing process becomes more difficult. Also, if the semiconductor package is manufactured using a newly changed substrate, many problems may occur due to defects caused by many problems typically occurring at the beginning of the manufacturing process.